Method and apparatus for generation of multiple uniform fluid filaments

ABSTRACT

Method and apparatus for generating a plurality of parallel droplet streams in a coating apparatus, such as an ink jet printing device, in which the streams break into droplets from fluid filaments at a uniform distance from issuing orifices. The streams issue from a pressurized chamber in which an elastic bending member is repetitively flexed by a plurality of parallel bending elements operated simultaneously to produce uniform bending throughout the effective length of said member to produce successive pressure disturbances within the supply chamber and induce varicosities of the same size and frequency in the issuing streams. This arrangement is able to enhance printing quality in an ink jet recorder by permitting maintenance of proper phase relationship between droplet formation and charging voltage.

United States Patent Titus et al.

1 51 Aug. 19, 1975 METHOD AND APPARATUS FOR GENERATION OF MULTIPLEUNIFORM FLUID FILAMENTS Assistant Examiner.lohn J. Love [75] Inventors:g 'la T g l lg g tfi Attorney, Agent, or FirmKenneth P. Johnson sao, paac 1n, 0 57 ABSTRACT [73] Assignee: International Business Machines Methd nd apparatus for generating a plurality of Corporation, Armonk,parallel droplet streams in a coating apparatus, such as [22] Filed: Jam10 1974 an ink jet printing device, in which the streams break intodroplets from fluid filaments at a uniform dis- PP NOJ 432,260 tancefrom issuing orifices. The streams issue from a pressurized chamber inwhich an elastic bending mem- [52] Us. CL 239/102, 239/566, 346/75 beris repetitively flexed by a plurality of parallel [51] Int. Cl BtiSb1/08 bending elements Operated Simultaneously to produce [58] Field 1023 l5 uniform bending throughout the effective length of 2, said memberto produce successive pressure disturbances within the supply chamberand induce varicosi- [56] References Cited ties of the same size andfrequency in the issuing streams. This arrangement is able to enhanceprinting UNITED S'liATES PATENTS quality in an ink jet recorder bypermitting mainte- 3,211,088 10/1965 Naiman 239/102 X name f properphase relationship between droplet iwzet ett 2:1. formation and chargingvoltage e e e a 3,700,169 10/1972 Naydan 239/4 14 Claims, 8 DrawingFigures 1e 1 m 4i 54 40 1 V 1 z 12 1 C 59% Q; I, so i r 51 QPATENTEUAUG-l ems 3.900.162

sum 1 UF 2 METHOD AND APPARATUS FOR GENERATION OF MULTIPLE UNIFORM FLUIDFILAMENTS BACKGROUND OF THE INVENTION This invention relates generallyto fluid droplet generation and more particularly to the generation ofparallel fluid droplet streams in which the streams change fromfilaments to droplets at the same distance from the issuing orifices.

In the construction of ink jet recorders having a plurality of parallelrecording streams of uniform velocities that are to each pass incharging relationship with a charging electrode, there is difficultyencountered in attempting to maintain the integrity of each stream as afilament to the same distance from the issuing orifice so that thestreams break into droplets at the same point and time. The droplets areselectively charged at the point of breakoff from the filament andsubsequently deflected along a desired trajectory downstream byelectrostatic deflection plates. Deflected droplets may be eitherrecorded or discarded depending on the printing mode. When thetransition point from filament to droplet changes, then the droplet doesnot form with the proper charge and hence is not deflected to thedesired impact point. The unpredictability of the drop breakoff point isespecially troublesome in multi-jet printheads where it is highlydesirable that the printing or non-printing of the plurality of jets ina row operate in synchronism.

Usually a single ultrasonic transducer is used to produce pressurevariations within ink supply chamber or manifold so that the difficultyis not with the synchronization of two or more transducers. When asingle vibrating transducer is used to stimulate drop formation,however, acoustical waves of generally varying intensity are present atthe issuing orifices. Thus, the filament lengths vary directly with theintensity of the stimulating pressure waves.

In the past. an attempt has been made to maintain uniform stimulatingpressure waves throughout the length of a row of orifices by mountingthe transducer at one end of the row of orifices so that the bendingwave resulting from the vibrating transducer is propogated along thelength of the plate. The ends of the plate are damped to inhibitvibrational reflections and maintain a relatively pure stimulationdisturbance. With this technique, the filament lengths become morenearly uniform but there still remains a difference between the lengthof filaments nearest the transducer and those farthest away. The moreremote filaments tend to be longer in length resulting in delayed dropformation and irregular charging.

It is accordingly a general object of this invention to provide an inkjet recorder of improved reliability and quality.

Another important object of this invention is to provide an ink jetrecorder in which the lengths of parallel filaments issuing from jetorifices are more nearly uniform so that droplets form at each filamentat approximately the same time and same distance from the orifices.

A still further object of this invention is to provide an ink jetmanifold with a vibrational transducer arranged therein such that inoperation uniform stimulating pressure changes are transmittedsimultaneously to all issuing orifices.

LII

Another object of this invention is to provide an ink jet manifold forissuing plurality of parallel fluid filaments having varicositiesinduced therein by a vibrating member in the supply chamber which isoperated in conjunction with a specially shaped chamber to increase theeffective amplitude of the generated acoustic waves.

SUMMARY OF THE INVENTION The foregoing objects are attained inaccordance with the principles of the invention by providing within apressurized ink supply manifold having a linear array of stream-issuingorifices, a flexible elastic bending member which is freely permitted tobend about a single axis. A plurality of piezoelectric transducers aresecured in a common orientation to one side of the bending member andall transducers are energized simultaneously from a common potentialsource to produce simultaneous bending of the member along its length.The member is preferably coextensive with the length of the manifold andparallel to the linear array of orifices through which pressurized inkis forced in parallel streams. The bending member has a spaced pair ofslits cut therein to provide a free boundary for the bending member andpermit more uniform movement of the bending portion. In the preferredembodiment, the bending member separates the manifold cavity into twocompartments, each specially formed to concentrate pressure wavescreated by the bending member at the two converging extremities of thecompartments.

The invention has the advantage of being capable of producing a bendingwave of uniform intensity along its length and along a linear array ofnozzles when the bending member is parallel therewith. Thus, the fluidissuing from the orifices can be subjected to a series of pressure wavesof uniform amplitude so that nearly identical varicosities are inducedin each stream at the same time. Because of this, the phase relationshipbetween charging voltages for the several streams and the drop formationis easier to maintain. This results in improved printing quality sincebetter registration of droplet impact is possible.

The foregoing and other objects, features and advan tages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded view of amarking head constructed in accordance with the principles of theinvention.

FIG. 2 is a perspective view of the marking head of FIG. 1 whenassembled.

FIG. 3 is a sectional elevation view of the marking head taken along thelines 33 in FIG. 2.

FIGS. 4a and 4b are rear elevation and plan views, respectively, of thevibrational bending member shown in FIGS. I and 3.

FIGS. 5a and 5b are schematic diagrams comparing streams issuing from aconventional marking head and one which incorporates the invention.

FIG. 6 is a front elevation view of an alternative embodiment of thebending member shown in FIGS. 40 and 4b.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1, 2 and 3,a marking head constructed in accordance with the invention comprisesgenerally a rear cavity block 10, a vibrational bending member 11, afront cavity block 12, an orifice plate 13. an insulative element 14,and a charging plate 35. Block is formed with a rear converging cavitywhile cavity 16 in block 12 is forwardly converging. When the two cavityblocks are secured together about member 11, there is formed asubstantially diamondshaped chamber which serves as a manifold forplurality of marking fluid orifices. Cavity 16 extends through block 12and forms a slot 17 in the front surface 18 of the block. Intermediateblocks 10 and 12 is a vibratory bending member 11 of a thin, flexible,elastic material such as stainless steel having a thickness ofapproximately 5 mils. The depth of each cavity 15 and 16 is preferablyone quarter of the wave length of the operating frequency of bendingmember 11. This depth produces a standing wave at each cavity extremity.

Bending member 11 is shown in greater detail in FIGS. 4a and 4b. Thebending member is generally rectangular and of sufficient size to besecured between blocks 10 and 12 and divide the manifold cavity into thefront and rear compartments l5 and 16. The member comprises generally ashaded marginal portion 20 which is gripped between the cavity blocks,and a similarly secured tab portion 21 of sufficient length to extendbeyond the outside edges of blocks 10 and 12 when assembled together. Acentral vibratory portion 22 of the bending member is cut free of themember proper by two slits 23 extending through the thickness of themember. This permits the vibratory center portion 22 to be free at itsends.

On one side of bending member 11 between slits 23 is placed a pluralityof transducers, preferably piezoelectric strips of a material such asbarium titanate. These strips are cut with a length to width ratiovarying from approximately 4:l to 6:1 and have a thickness ofapproximately 10 mils. The length of the transducer strips 24 ispreferably approximately the length of the slits 23 which can in turnvary according to the amount of bending deflection desired within cavitycompartments l5 and 16. The piezoelectric material is preferablyselected for maximum bending. As is shown in FIG. 3, transducer strips24 extend beyond the upper and lower limits of compartments l5 and 16but may be shortened to less than the edges of the compartments properadjacent bending member 11. The relatively large length to width ratiois desirable for the piezoelectric strips in order to maximize bendingof central portion 22 about its longitudinal axis. The piezoelectricmaterial is mounted for expansion in the thickness mode only and whenenergized will tend to bend in a dish-shaped manner. The narrow width ofeach transducer finger tends to minimize the effect of the dishing andthus produce single axis bending.

Transducer strips 24 are secured to central portion 22 of bending member11 by an adhesive such as a bonding epoxy. The number and spacing of thetransducer fingers 24 will be determined, as mentioned above,by therequired deflection of central portion 22 to effect the necessarypressure waves within the issuing fluid. Transducer fingers 24 aremounted with the same orientation, of course, so that all transducerswhen energized will effect a bending force inunison on central portion22. The transducers should be evenly spaced and parallel to relief slots23. After the transducer fingers have been mounted to element 11, thevoids between the fingers are filled with a suitable adhesive such asepoxy. Thereafter, each of the fingers is electrically connected via aconductor 25 soldered to the exposed outside surface of each of thefingers and to a terminal block 26. The terminal block is secured with asuitable insulative adhesive to bending member 11. At terminal block 26,an insulated conductor 27 is connected with the wire 25 and secured withan adhesive along tab 21. Thereafter, transducers 24 and wire 25 arecoated with an insulative protective material which serves also as amoisture seal. A polyurethane or other suitable material may be used.

Bending member 11 with transducer fingers 24 thereon is mounted betweencavity blocks 10 and 12 using a pair of gaskets 30 as shown in FIGS. 1and 3. A recess 31 is preferably provided in one of the cavity blockssuch as block 10 to allow tab portion 21 of bending member 11 andconductor 27 to extend below the lower surface of the block forattachment to suitable electrical signal generating source 28, such as asinewave generator. By using a conductive bending element and adhesivefor mounting fin gers 24, the energizing circuit issimplified. Blocks 10and 12 are preferably secured together with screws placed so as toprevent leakage of a pressurized fluid within the cavity. Orifice plate13 is secured to the rear surface of insulative element 14 with anadhesive and both are then secured to front surface 18 of cavity block12 with suitable means such as screws (not shown). A gasket 31 is usedto provide a seal. Thereafter, insulative plate element 14 with openings34 aligned with orifices 33 is secured to orifice plate 13. Theinsulative element 14 is used to allow subsequent attachment of chargingplate 35 containing charge rings 36 with which fluid droplets can beselectively charged as they break off from filaments extending fromorifices 33. Orifices may range in size from 0.5 to L5 mils in diameterwhileholes 34 are larger, such as 6 to 8 mils. 1

After the marking head has been assembled, it is connected to a suitablepressurized ink supply as indicated by pump 37 and duct 38 which areconnected with inlet opening 38 that communicates along a groove withcavities 15 and 16 as shown in FIG. 3. Vents 43 with stoppers 44 permitbleeding off of air during charging. Since the two cavities areinterconnected by slits in bending member 22, the manifold is equallypressurized in both compartments providing balanced static pressures.Tab portion 21 of bending member 11 and the conductor 27 extendingbeyond the bottom of the marking head are connected across the signalsource sinewave generator 28, that is capable of applying an actuatingsignal, for example, from to Khz, to piezoelectric transducer fingers24.

As pressurized ink is forced from the linear array of orifices 33, thepulses applied to piezoelectric transducers 24 cause central portion 22of the bending element to deflect to a position such as shown by dottedline 40 in FIG. 3. The signal generator may operate between ground andsome voltage or be connected so as to operate as voltage swings aboutthe ground level. If the latter condition is used then, of .course.bending member deflection will be between the pair of dotted. lines 40and 41. The energization of transducers 24, by

causing central portion 22 to repetitively flex sets up pressure waveswithin converging compartments l5 and 16 causing the ink at each of theorifices to experience a change in pressure simultaneously along theorifice array. This causes the occurrence of varicosities in the fluidfilament issuing from each orifice which results in the formation ofdroplets in each stream at the same distance from orifice plate 13.

Referring to FIGS. 5a and b, there'is illustrated for comparativepurposes a schematic representation of droplets formed by prior art,vibratory devices and those formed with structure assembled inaccordance with the invention. It will be noted that fluid streams 50issuing from the orifice plate, FIG. 5a as in the prior art tend tobreak up at a varying distance from the orifice plate within the chargeplate. The breakup for the filaments into droplets occurs usually in apattern which is reflective of the variations in wave intensity at theorifice plate and along the orifice array direction. When the vibratoryelement 11 as disclosed above is used within the ink manifold, eachfluid filament 51 has induced therein at the same time and with the samemagnitude a pressure variation which results in similar varicositiesoccurring along each filament as it issues from the orifice. This hasthe advantage of resulting in droplet breakoff at the same point andtime within the charge plate. By using the latter structure, much of thedifficulty in maintaining the proper phase relationship in both time andspace between corresponding drops of the array of filaments is obviatedwith the result that droplets are more accurately registered on arecording surface.

In FIG. 6 there is shown a modification of bending element 11 in whichstiffening bars 45 are added transversely of transducer fingers 24 andon the opposite side of central flexing portion 22. The stiffening barsare optional and used only if portion 22 tends to bend transversely ofthe desired bending. Bars 45 may be adhesively secured to element 11.Also, the bars may be replaced with a corrugated shim stock toaccomplish the same result. The preferred material is stainless steel ineither case so as to prevent corrosion. Other metals, however, may beused if desired.

Although bending element 11 has been shown secured on all edges aboutthe flexing portion 22, it can be secured only along opposite edges oralong a single edge, preferably an edge parallel to the bending axis.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. Apparatus for producing a plurality of parallel streams of fluiddroplets comprising:

means providing a cavity for receiving pressurized nozzle means along awall of said cavity means having at least one row of orifices therein;

means for supplying fluid under pressure to said cavity so that saidfluid flows through said orifices in parallel streams;

means within said cavity for generating a series of pressuredistrubances therein, said generating means including a flexible memberand a plurality of independently movable elements cooperably bendingsaid member to produce a said pressure disturbance when moved; and

means for simultaneously and repetitively moving said elements to createa said pressure disturbance along said nozzle row, thereby creatingpressure perturbations within said issuing streams.

2. Apparatus as described in claim 1 wherein said elements are alignedon said flexible member in a row parallel to said orifices.

3. Apparatus as described in claim 2 wherein said member is a planarmember secured along an edge thereof in said cavity forming means.

4. Apparatus as described in claim 3 wherein said elements are parallelpiezoelectric strips commonly secured on said planar member.

5. Apparatus as described in claim 1 wherein said planar member is fixedalong its periphery in said cavity forming means with a major surfacethereof parallel to said nozzle row, and said elements are piezoelectricstrips commonly secured to the opposite major surface of said member ina row extending parallel with said nozzle row.

6. Apparatus as described in claim 3 wherein said member is fixed at itsperiphery in said cavity forming means so as to divide said cavity intofirst and second compartments, and said member includes at least twoopenings therein to interconnect said two compartments.

7. Apparatus as described in claim 6 wherein said opposite walls of eachcompartment converge as a function of the distance from said flexiblemember.

8. Apparatus as described in claim 7 wherein said nozzle means issecured along a surface of one of said compartments opposite said planarmember.

9. Apparatus as described in claim 4 wherein said planar member includesat least one stiffening component secured thereto on the surfaceopposite said elements and is oriented in a direction transverse to thelongitudinal axis of said elements.

10. Apparatus as described in claim 7 wherein said compartment wallsconverge at a point approximately equal to one quarter of the wavelength of the operating frequency of said elements.

11. Apparatus for producing a plurality of parallel streams of fluiddroplets comprising:

means for providing a cavity for receiving pressurized fluid therein;

nozzle means along a wall of said cavity means having a row of orificestherein for issuing parallel streams of fluid;

means for supplying pressurized fluid to said cavity to produce saidstreams;

means within said cavity for generating a series of pressuredisturbances therein, said generating means including a flexible memberbendable about an axis parallel with the longitudinal axis of saidorifice row; and

bending means energizable to bend said member about said axis.

12. Apparatus according to claim 11 wherein said bending means comprisespiezoelectric material.

13. Apparatus according to claim 11 wherein said flexible member issecured along its periphery and has a pair of slits therein normal tosaid bending axis.

14. Apparatus according to claim 11 further including means forenergizing said bending means to create a pressure disturbance alongsaid row.

1. Apparatus for producing a plurality of parallel streams of fluiddroplets comprising: means providing a cavity for receiving pressurizedfluid; nozzle means along a wall of said cavity means having at leastone row of orifices therein; means for supplying fluid under pressure tosaid cavity so that said fluid flows through said orifices in parallelstreams; means within said cavity for generating a series of pressuredistrubances therein, said generating means including a flexible memberand a plurality of independently movable elements cooperably bendingsaid member to produce a said pressure disturbance when moved; and meansfor simultaneously and repetitively moving said elements to create asaid pressure disturbance along said nozzle row, thereby creatingpressure perturbations within said issuing streams.
 2. Apparatus asdescribed in claim 1 wherein said elements are aligned on said flexiblemember in a row parallel to said orifices.
 3. Apparatus as described inclaim 2 wherein said member is a planar member secured along an edgethereof in said cavity forming means.
 4. Apparatus as described in claim3 wherein said elements are parallel piezoelectric strips commonlysecured on said planar member.
 5. Apparatus as described in claim 1wherein said planar member is fixed along its periphery in said cavityforming means with a major surface thereof parallel to said nozzle row,and said elements are piezoelectric strips commonly secured to theopposite major surface of said member in a row extending parallel withsaid nozzle row.
 6. Apparatus as described in claim 3 wherein saidmember is fixed at its periphery in said cavity forming means so as todivide said cavity into first and second compartments, and said memberincludes at least two openings therein to interconnect said twocompartments.
 7. Apparatus as described in claim 6 wherein said oppositewalls of each compartment converge as a function of the distance fromsaid flexible member.
 8. Apparatus as described in claim 7 wherein saidnozzle means is secured along a surface of one of said compartmentsopposite said planar member.
 9. Apparatus as described in claim 4wherein said planar member includes at least one stiffening componentsecured thereto on the surface opposite said elements and is oriented ina direction transverSe to the longitudinal axis of said elements. 10.Apparatus as described in claim 7 wherein said compartment wallsconverge at a point approximately equal to one quarter of the wavelength of the operating frequency of said elements.
 11. Apparatus forproducing a plurality of parallel streams of fluid droplets comprising:means for providing a cavity for receiving pressurized fluid therein;nozzle means along a wall of said cavity means having a row of orificestherein for issuing parallel streams of fluid; means for supplyingpressurized fluid to said cavity to produce said streams; means withinsaid cavity for generating a series of pressure disturbances therein,said generating means including a flexible member bendable about an axisparallel with the longitudinal axis of said orifice row; and bendingmeans energizable to bend said member about said axis.
 12. Apparatusaccording to claim 11 wherein said bending means comprises piezoelectricmaterial.
 13. Apparatus according to claim 11 wherein said flexiblemember is secured along its periphery and has a pair of slits thereinnormal to said bending axis.
 14. Apparatus according to claim 11 furtherincluding means for energizing said bending means to create a pressuredisturbance along said row.